Given the second order non-homogeneous linear differential equation y+2y-3y 3 ex+ 4 cos x, (notation e^x= exp(x) = "e raised to the x power, cos x="cosine of x") find a particular solution yp of the non-homogeneous equation.

For the PI how do I use the inverse operator when I write

3e^x/(1+3)(D-1)+4cosx/(D^2+2D-3)

3/4e^x/D-1+4cosx/-1+2D-3

3/4 x!/1! e^x + 4 cos x/-4+2D=3/4xe^x+2cosx/D-2

Using PI of 1/D-alphaQ = e^alpha x integrate e^-alpha Qdx. 
how do I proceed from there the steps for finding PI answers the full solution